docs: def make2d(array, cols=None, dtype=None):
      '''
      Make a 2D array from an array of arrays.  The `cols' and `dtype'
      arguments can be omitted if the array is not empty.
  
      '''
      if not len(array):
          if cols is None or dtype is None:
              raise RuntimeError(
                  "cols and dtype must be specified for empty array"
              )
          return _np.empty((0, cols), dtype=dtype)
      return _np.vstack(array)